I currently use a 1911 45 cal five inch barrel, but this weighs about 3.5 lbs including holster & extra mag. Is there something lighter to carry and still have penetration to stop a 300 lb hog?

The biggest hog I ever killed field-dressed at over 350 lbs (the limit of the scale). I dropped him with a .22LR at a range of about 15 feet. He looked up at me and I popped him in the center of the forehead. He dropped like a switch had been thrown and it took four of us to drag him out of the thicket to where we could get him on a vehicle. We weighed him back at camp, sans his innards and that's when the topped-out the scales.

The guys I used to hunt with, though favored something a little heavier for hog hunting on horseback. Almost every one of them carried the .22WM. Headshots only, preferably when the hog is looking at you. Draw an imaginary X from eyes to ears and put a bullet in the center of the X. They drop right there.

The problem comes when you try to take a shoulder shot. If the hog's been running wild for a while, he'll have a big shield of matted hair, gristle, and pine sap over the shoulder area. However, the head shot offers the best chance of anchoring him on the spot.